Among 26,294 hospitalized medical patients monitored by the Boston Collaborative Drug Surveillance Program, 46% received at least one intramuscular (IM) injection. Drugs for which IM injection was the route of administration in more than 80% of all exposures included penicillin G procaine, mercurial diuretics, cyanocobalamin, streptomycin sulfate, colistimethate sodium, meperidine hydrochloride, cephaloridine, scopolamine hydrobromide, kanamycin sulfate, and iron dextran injection. Local complications of IM injection were reported in a total of only 48 patients (0.4% of all IM recipients). Local complications were most commonly associated with IM injection of cephalothin sodium. Clinically important local complications are uncommonly associated with IM injections in general. However, certain drugs, eg, cephalothin, produce injection-site complications with relatively high frequency; the clinical role of IM injection of such drugs should be reevaluated.